Apparatus for treating contaminated gas

ABSTRACT

Contaminated air is treated to attain a predetermined temperature, purity and relative humidity using an apparatus which includes heat exchange elements and water spray nozzles. The heat exchange elements comprise tubes arranged to impart turbulence to the contaminated air flowing over the tubes. Water is sprayed into the air flow against the tubes and water droplets intimately mix with the air flow so that the contact surfaces of the tubes simultaneously perform three functions: purification of the air, humidification of the air to a relative humidity of about 100%, and bringing the air to a desired temperature. Purification occurs when the air-water droplets hit the outside contact surfaces of the tubes. Impurities contained in the air are deposited on the contact surfaces to be washed away by the water spray. Humidification occurs when the spray water on the contact surfaces is vaporized by the addition of heat from a heat transport fluid conducted through the tubes. The treated air can be heated to its desired final temperature and relative humidity in a separate heater downstream of the apparatus.

This is a continuation of application Ser. No. 380,744, filed May 12,1984 now abandoned.

The present invention relates to treating a contaminated gas, inparticular a gas at elevated temperature and in most applications air,to purify the gas and give it properties to make it reusable. Inparticular, the invention relates to the treatment of air to give it aselected degree of purity, a predetermined temperature and apredetermined relative humidity, simultaneously making possible adiminution of the heat consumption required to make the air suitable foruse in heating a living space.

Within many industries, there is a demand for processing air as well asfor inlet air to industrial buildings having accurately selectedtemperature and relative humidity. The air, at least as far as it is tobe used as inlet air for heating living space, is subject to exactingstandards of purity. As typical examples of such industries where highrelative humidity is a must there are the textile industry, weavingindustry, and paper industry, because in such industries dry air createssevere problems of static electricity. As a byproduct of suchindustries, large flows of air of elevated temperature are produced,which air may be more or less contaminated. Theoretically, it would seemdesirable at least during winter to utilize the heat content of such airby purifying and reconditioning it, with respect to its temperature andrelative humidity, and then recirculating it to the living spaces or forreuse in the industrial process that created it.

It is known in the prior art to scantily purify such heated andcontaminated air, that is, to purify it only so far is required to avoidenvironmental problems, and then to expel the air into the surroundingatmosphere. To satisfy the demand for inlet air for heating, it has beencommon practice to use large quantities of fresh air from thesurrounding atmosphere. But, at least during winter, large amounts ofenergy must be added to fresh air for the required net temperatureincrease and for vaporization of the quantities of water required toincrease the very low moisture content of the air.

It is an object of the present invention to substantially eliminate suchproblems by simultaneously providing for a purification of, a heatrecovery from and a recirculation of heated outlet air in such a mannerthat the outlet air alone or admixed with a quantity of fresh air,treated in the same manner, attains a desired purity, temperature andrelative humidity.

Said object is attained according to the invention by executing a methodor using an apparatus as defined by the accompanying claims.

The invention will be more closely described with a reference to theaccompanying drawings, in which

FIG. 1 schematically illustrates an apparatus for carrying out themethod according to the invention.

FIG. 2 is a simplified cross-section of an embodiment of the first stageof an apparatus laid out as illustrated by FIG. 1, and

FIG. 3 illustrates in additional detail the apparatus shown in FIG. 2.

The invention enables saving large energy quantities by cleaning,climatizing and recirculating outlet air from different kinds ofprocesses. Energy savings can be provided by means of a direct heatrecovery from the warm outlet air and due to the fact that the processair, at least in part, is recirculated. The heat content of the processair is used as a substitute for the heat bound by the vaporization ofsuch quantities of water which are necessary for increasing the relativehumidity of the air to a desired value.

According to the invention the process air, possibly admixed with freshair from outside, is conducted through a flow duct enclosing a number ofcontact or deposition surfaces, onto which are deposited and collectedsuch impurities as have been carried by the gas or have been dissolvedtherein or admixed therewith. In a preferred embodiment of theinvention, the gas is conducted in such a manner that the contactbetween the gas and said contact surfaces will be intimate, and,further, in such a manner that the gas repeatedly is forced to changeflow direction, so that particles, droplets of liquid or similar itemscarried by the gas, due to their relatively high density, hit thesurfaces. According to the invention the purification of the gas isprovided for by means of wet-scrubbing, in which the liquid, in mostapplications water, is ejected into the gas, preferably incountercurrent thereto, and, as the case may be, onto portions of saidcontact surfaces. To enhance the efficiency of the scrubbing, thescrubbing liquid may contain substances without properties detrimentalto the environment, tensides, e.g., which provide for an emulgation ofthe air impurities in the scrubbing liquid. To provide for thepurification of the gas for extended periods of time, a substantiallycontinuous cleaning of the contact surfaces is an object of theinvention. Accordingly, cleaning is effected by using liquid injectedinto the gas and onto the contact surfaces to continuously flush awaythe impurities as they are separated from the gas. Advantageously, asurplus of scrubbing liquid may be used for this purpose. After havingbeing used for wet-scrubbing and for the removal of separatedimpurities, the liquid is collected, and a concentrate of impuritiestogether with a portion of the scrubbing liquid is separated andreplaced by a corresponding quantity of pure liquid. This surplus ofscrubbing liquid has a function to be described in more detail below.

The invention aims not only at purification of a gas flow that it can berecirculated and used for heating a living space, but also an adaptionof the temperature and relative humidity of the gas to values requiredfor an industrial process. It is made possible by injecting a surplus ofwater over contact surfaces of a heat exchanger and by transferring heatto or from the gas via said contact surfaces to create a gas flowsaturated with humidity and accurately heated to a predeterminedtemperature level. By later adding heat, such gas flow may then bysimple means be brought to predetermined values of relative humidity andtemperature. Such heating of the gas flow is, in a preferred embodimentof the invention, provided for in a separate heater stage, but may aswell be provided for by injecting the saturated air into the space to beheated where the heating is then provided by surplus heat fromequipment, machines or the like present in the locality.

When moistening the air into a saturated state, very large quantities ofvaporized water are necessary, during winter-time in particular, iffresh air is introduced from the surrounding atmosphere. Such largequantities of water bind large quantities of energy, which energy is,according to the invention, in the first instance taken from thecontaminated gas being treated according to the invention.

To improve the heat transfer to or from the gas at the contact surfacesas far as possible, a heat transporting fluid is conducted along oneside of said surfaces, while the gas or air is conducted along the otherside thereof. Preferably, the flow directions are selected according tothe counter-current principle, combined, if desired, with the crosswiseflow principle, which makes possible maximum temperature changesrelative to the contact surface. The heat transfer between the gas andthe heat transporting fluid passing through the contact surface isfurther enhanced by wetting the other side of said surface with afilm-like coating of scrubbing liquid. The heat transfer between the gasand the contact surface may also be enhanced by using a high velocity ofand turbulence in the gas flow, which turbulence is also advantageouswith respect to the efficiency of the separation of gas impurities.

A comparatively large contact surface which is inert relative to thetreated gases and scrubbing liquid is necessary to obtain the maximumefficiency of the scrubbing. When the contact surface is made from amaterial having excellent heat conducting properties, copper forinstance, the contact surface will be too large relative to the heattransfer capacity if the contact surface has a sufficient size to beefficient as regards the purification function. For an economic point ofview, it would hardly be desirable to use a contact surface of anexpensive metal material with sufficient size to obtain the intendedpurification. Therefore, a sufficiently large and inert contact surfaceis obtained by using a plastic material, as will be explained in moredetail below.

FIGS. 1-3 illustrate an apparatus for executing the method according tothe invention. FIG. 1 shows that the apparatus comprises a first stage 1and a second stage 2. The first stage constitutes an apparatus acting asa combined heat exchanger and scrubber which provides a purified airflow saturated by humidity and having a predetermined temperture at itsoutlet. Stage 1 has an air inlet A, an air outlet B, an inlet 3 for thesupply of heat transporting fluid and an outlet 4 for said fluid. Theinlet and outlet for the heat transporting fluid are connected tocontact surfaces 5 constituting of tubular elements through which theheat transporting fluid flows from the inlet 3 to the outlet 4, that is,in countercurrent to the air flow from the air inlet to the air outletof stage 1. It is also advantageous to arrange the tube system such thatthe flow is in accordance with the crosswise current principle. Further,stage 1 comprises injection means 6 for injecting a finely distributedscrubbing liquid, said liquid in a majority of applications being awater spray. The injection means 6 is arranged so as to inject theliquid into the air flow proper, preferably against the directionthereof, as well as onto the surfaces 5 to apply thereto a film-likecoating of liquid. Stage 1 further comprises a tray 7 for collectingsurplus liquid. The liquid collected in the tray 7 is fed back to theinjection means 6 by a pump 8. Part of the quantity of liquid is removedand a corresponding quantity of pure liquid added to provide forrecirculation of substantially the same volume of liquid.

The contact surfaces 5 of stage 1 serve two different aims. First, thesurfaces 5 constitute heat exchange surfaces to transfer heat to or fromair entering at inlet A. This heat is transferred through surfaces 5between the air and a heat transporting fluid flowing from inlet 3 tooutlet 4. Secondly, the surfaces 5 provide surfaces that bring intocontact injected liquid and the air flow, thus enhancing thevaporization of the injected water while binding the impurities enteringwith the air. Preferably, the surfaces 5 are arranged in such a mannerrelative to each other that they give rise to repeated changes ofdirection in the flowing air.

Due to the fact that the invention is mainly, although not exclusively,related to the treatment of such contaminated air of elevatedtemperature which, at least together with water, may be corrosive andwhich shall be purified from contaminations to such a degree that it canbe re-used as inlet air for heating living spaces, certain conditionswill have to be satisfied by stage 1 of the apparatus. The requirementof purification (i.e. scrubbing) implies that there are large contactsurfaces between the air and injected liquid. This is also in agreementwith the conditions for a favorable heat exchange and a satisfactoryvaporization of injected water. However, corrosion resistant materialsare so expensive that a sufficiently large surface is hardly attainableby using conventional materials. Therefore, according to the invention,corrosion resistivity is provided by manufacturing the heat exchangerand contact surfaces 5 from an artificial resin material. The use ofsuch a material may seem remarkable in this connection, since mostplastic materials have poor heat conductivity and thus impair theefficiency of the heat exchange. However, such plastic materials arecomparatively cheap and have satisfactory corrosion resistance and atlow cost can be made so large that, in spite of their poor heatconducting capacity, the efficiency of the heat exchange is maintainedat a sufficiently high level. Also favorable for attaining a highefficiency is the fact that the surfaces when made of such materialoperate in a wetted state.

Outlet B of stage 1 also constitutes an inlet to the second stage of theapparatus, constituting a heat exchanger 2 which has an outlet C. Stage2 includes an inlet 9 for a heat transporting fluid in order to heat thesurfaces 11, which fluid leaves the heat exchanging surfaces 11 throughan outlet 10. The heat exchanging surfaces 11 are arranged according tothe counter-current principle.

The apparatus may further comprise a droplet separator, not shown inFIG. 1, which may either be arranged within the combined scrubber andheat exchanger stage 1 or as a separate unit between stages 1 and 2 inthe connection therebetween at outlet B.

In accordance with the invention this is provided for as follows. In thefirst stage 1 of the apparatus, water is injected by spraying via theinjection means 6 in such a quantity and in finely distributed statethat the relative humidity of the air increases to a value substantiallyreaching 100% at outlet B. Due to the vaporization of the water, acertain quantity of energy will then have been absorbed. As a result, atoutlet B the air is saturated by humidity and has a lower temperaturethan would be the case at outlet A, although the abosrbed energy ispartly substituted via the contact surfaces 5. If no further water ispresent in the form of minute water droplets, the quantity of watercontained in a specific volume of air is determined by the temperatureof the air. To change the values as to relative humidity and temperaturefrom the values prevailing at outlet B to the intended final values atoutlet C, the temperature is increased to a desired level by the heatsupplied by the heat exchanger stage 2. The maximum quantity of watercontained in a specific volume of air in the form of vapor beingdependent on the temperature (i.e., increasing with the temperature),the relative humidity of the air will decrease to a value at outlet Cless than 100% when the temperature is increased. The magnitude of thedecrease of the relative humidity will be dependent on the absolutemoisture content of the air, this in its turn being dependent of thetemperature prevailing at outlet B. This means that, after thetemperature at outlet C is determined, the relative humidity at thisoutlet C may easily be controlled by controlling the air temperature atoutlet B. To provide for such control of the temperature at outlet B, atemperature sensor 12 is disposed there, which temperature sensor 12controls a control valve 13, which is, preferably, arranged in the fluidoutlet 4 of stage 1. Obviously, a certain amount of control of thetemeprature may also be provided by controlling the temperature of theentering air flow, that is, by varying the proportion of cold airadmixed from the outside, for instance, with the warm process air.Finally, the air temperture at outlet C is controlled in a similarmanner by sensing the temperature by means of a sensor 14 arranged inthe outlet, outlet C, of the apparatus which controls a control valve 15in the heat transporting fluid duct of stage 2.

In such operating situations when the air at inlet A has a comparativelyhigh temperature, the temperature control at outlet B provides for heattransport from the surfaces 5 by means of the heat transporting fluidentering at 3 and leaving at 4, that is, the heat transporting fluid isheated by the air if the cooling due to the vaporization of the injectedwater is not sufficient for decreasing the air temperature. In otherconditions of operation, in which air entering at inlet A has a lowertemperature or is drier (for example, operation during winter-time) heatis instead added to the air flow.

FIG. 2 shows a cross-section of an embodiment of the combinedpurification and climatization apparatus, that is, stage 1 in FIG. 1.The apparatus is built up about an upper and a lower plate 16 and 17,respectively, which are secured relative to each other by means notshown in FIG. 2 which, for instance, comprise the vertical postsarranged along the peripheries of the plates 16 and 17 shown in FIG. 3.Between the plates a number of tube coils 18 are arranged, the innerends of which are connected to an outlet 19 and the outer ends of whichare connected to an inlet 20, thereby providing for a counter-currentaction as well as a crosswise-current action relative to the flow of airto be purified and provided with the selected climate parameters. Thecoils 18 are arranged in such a manner that a vertical channel 21 isprovided centrally of the apparatus, said channel in practice having adiameter on the order of 1 meter, for instance. Said channal 21 opensdownwardly, the plate 17 having a corresponding aperture 22, connectingto an air supply duct 23 comprising the inlet A. From inlet A air flowsthrough the aperture 22 into the channel 21 and further radiallyoutwardly through the passages D formed between adjacent ones of coils18 to the periphery of coils 18 where the air leaves the apparatus.

At the periphery of the central channel 21 a number of vertical tubes 24are arranged, which tubes are, on top of the plate 16, connected to aninlet header 25 for introducing scrubbing fluid, usually water, underpressure. In an embodiment of the size referred to above, the verticaltubes 24 may be arranged at a mutual distance of about 10 cm in theperipheral direction, the tubes on their surfaces facing the coils beingprovided with a number of nozzles 26 to eject jets of finely dispersedwater toward the coils 18 and into the passages D within which the airflows radially outwardly. Water is added in such a quantity that thecoils 18 are covered by film-like layers of water and, in additionthereto, the air is intimately admixed with the finely dispersed waterejected through the nozzles 26. The water is thus expelled over theperiphery of the device together with the impurities separated from theair and is thereafter collected to be purified and recirculated. Asurplus of water may be used to effectively wash the coils 18 and thuskeep the coils free from the precipitated contaminants.

As an alternative to the vertical tubes 24 as described, the channel 21may comprise a centrally arranged tube provided with a number of nozzlesfor ejecting finely dispersed water. Said nozzles are then preferablydirected against the air flow from the air supply duct 23 as well asagainst the coils 18. Preferably, the nozzles are of the self-rinsingspiral type.

Instead of being shaped in the manner illustrated by FIG. 2 the coils 18may also be shaped in a plurality of alternative manners. So forinstance, the coils, instead of being arranged as flat spirals, may beconical- or screw-shaped, the different windings of the coils beingarranged relative to each other in such a manner that the flow in theradially outwardly direction through passages D between coils 18 will be"wave-shaped" or "zigzag-shaped" that is, repeatedly change direction.Further, the nozzle 26 instead of being arranged in the manner describedabove, may be located along a coil within the central channel 21.Further the economic advantage in providing a sufficiently large surfaceof the coils 18 by producing them from a plastic material is emphasized.

FIG. 3 shows an example of a construction of the combined contaminationseparator and climatization apparatus, that is, stage 1 in FIG. 1, asapplied in practice. Above and below an air admission channel 23 anupper and a lower group of tube coils 18 are arranged, the upper groupcorresponding to the device illustrated by FIG. 2. FIG. 3 shows that theupper as well as the lower group of tube coils 18 are arranged betweenupper and lower plates 16 and 17, respectively, and are in connectionwith an outlet 19 and an inlet 20 for heat transporting fluid. Waterunder pressure is introduced by pumps 8 to the inlet tube 25 andtherefrom via vertical tubes 24 to nozzles 26 within the central channel21. The air introduced at A leaves along the peripheries of the coils 18passing therefrom through a droplet separator 27 to the outlet B.Preferably the apparatus as well as the droplet separator are enclosedby a cover 28, the lower part of which acts as collecting tray 7 forsurplus water as shown schematically in FIG. 1. As mentioned above withreference to FIG. 2, the greater part of the water ejected through thenozzles 26 leaves at the periphery of the coils, there containing theprecipitated impurities washed from the coils. However, part of thefinely dispersed water, if injected in large surplus, might be carriedon by the air flow, due to the fact that said flow has a relatively highflow velocity. In the embodiment according to FIG. 3 the two heatexchanger-scrubber units are enclosed in a cover presenting a large flowcross-section for the air, the flow velocity thus being substantiallydiminished to allow for a settling of the water particles carried by theair toward the bottom of the cover to the collecting tray 7. Very smallparticles which have not yet been precipitated when leaving the cover 28will be separated out in the droplet separator 27, so that the airleaving the apparatus through outlet B is substantially saturated withhumidity but is free from water in the liquid state.

The invention may be modified within the scope of the appended claims.

I claim:
 1. An apparatus for treating air contaminated with impuritiesby scrubbing, humidifying and tempering the air to provide air having apredetermined degree of purity, a relative humidity of substantially100% and a predetermined temperature, the apparatus comprising an inletfor contaminated air, an outlet for purified air and a flow paththerebetween; injection means for injecting a spray of liquid into saidflow path; and heat exchanger means in said flow path for providingcontact surfaces having one side in contact with said spray and said airand another side in contact with a heat transporting fluid, wherein:saidflow path extends from said inlet to said outlet radially outwardlythrough said heat exchanger means for directing air along said flowpath; said heat exchanger means comprises first and second pluralitiesof axially stacked layers of coils of tubular elements, said pluralitiesbeing axially spaced from one another, each said layer includingradially inner and outer coils interconnected for the passage of saidheat transporting fluid through said tubular elements from a coil inletmeans connected to said outer coils to a coil outlet means connected tosaid inner coils; said injecting means comprises first and secondpluralities of injection nozzles disposed radially inwardly of saidfirst and second pluralities of coils, respectively, for directing saidspray thereagainst; and said inlet includes first and second inlet ductspositioned and arranged for directing contaminated air across said firstand second pluralities of coils generally radially outwardly thereof. 2.An apparatus for treating air contaminated with impurities by scrubbing,humidifying and tempering the air to provide air having a predetermineddegree of purity, a relative humidity of substantially 100% and apredetermined temperature, the apparatus comprising an inlet forcontaminated air, an outlet for purified air and a flow paththerebetween; injection means for injecting a spray of liquid into saidflow path; and heat exchanger means in said flow path for providingcontact surfaces having one side in contact with said spray and said airand another side in contact with a heat transporting fluid, wherein:saidheat exchanger means comprises a plurality of axially stacked layers ofcoils of tubular elements, each said layer including radially outer andinner coils respectively interconnected for passage of said heattransporting fluid through said tubular elements; said flow path extendsfrom said inlet to said outlet radially outwardly through said heatexchanger means for directing air along said flow path; said injectingmeans comprises a plurality of parallel pipes arranged in a ringradially inwardly of said inner coils for directing said spray at saidtubes; and said heat exchanger means includes a coil inlet connected tosaid outer coils and a coil outlet connected to said inner coils.